Australopithecus sediba – This small human species, which existed around 2 million years ago, displayed a blend of ape-like and human-like traits. Homona Lady – A recent study led by Dr. Samar Syeda from the American Museum of Natural History reveals that this newly identified species, dating back approximately 335,000 to 236,000 years, shows a distinct pattern of bone thickness, indicating diverse load applications and potential grip types.
A reconstruction depicting the life of Australopithecus sediba commissioned by the University of Michigan Museum of Natural History. Image credit: Elisabeth Daynes/S. Entressangle.
Dr. Syeda and her team explored variations in phalanx morphology, discovering that South African hominins might exhibit different dexterities along with varied climbing abilities.
They focused on two nearly complete fossil hand skeletons discovered in South Africa: the hands from Australopithecus sediba, dated at 2 million years old, and hand skeletons from the newly identified star cave system from 250,000 years ago.
While no direct associations with stone tools have been established for either species, certain aspects of their hand and wrist morphology imply a level of dexterity that aligns more closely with human hands than with those of chimpanzees and gorillas.
“Stone tools have been found in South Africa dating back at least 2.2 million years (and potentially as far back as 3.3 million years),” stated Dr. Tracy Kivell, a researcher at the Max Planck Institute for Evolutionary Anthropology and Witwatersrand University. “Many primates are adept stone tool users, as are Australopithecus sediba and Homona Lady.
“However, the exact nature of their tool usage and interaction remains unclear.”
Furthermore, both Australopithecus sediba and Homona Lady exhibit ape-like characteristics, especially within their upper limb bones, which could be advantageous for climbing.
The ongoing debate in paleontology considers whether these traits indicate actual climbing behaviors or if they are simply evolutionary remnants from climbing ancestors.
Reconstruction of Homona Lady‘s head by artist John Gurche, who spent around 700 hours recreating it from a bone scan, published in collaboration with the University of Witwatersrand, the National Geographic Society, and the South African National Research Foundation in the journal Elife. Image credits: John Gurche / Mark Thiessen / National Geographic.
To explore these inquiries, researchers examined variations in the internal composition of the fingers (cortical bone) in both Australopithecus sediba and Homona Lady.
Bones are dynamic tissues that can modify their structure based on usage and loading throughout life, thickening in high load areas while thinning in regions subjected to lesser loads.
As such, variations in internal cortical thickness can shed light on how these two hominin fossils utilized their hands during their lifetimes.
“Our findings indicate that both Australopithecus sediba and Homona Lady exhibit a range of functional signals within the cortical bone structure of their fingers,” remarked Dr. Syeda.
In Australopithecus sediba, the distribution of cortical bones within the proximal and intermediate phalanges of most fingers closely resembles that of apes. However, the thumb and pinky bones are more akin to human bones.
“These two digits appear to represent potential functional signals because they experience less frequent or lower loads during climbing or suspension,” noted Dr. Syeda.
“Combining these findings with a human-like thumb suggests that Australopithecus sediba employed its hands not just for climbing, but also for tool use and other dexterous activities.”
Homona Lady, in contrast, displays an unusual pattern where the proximal phalanx (the bone supported by the palm) shows human-like traits, while the intermediate phalanx (the bone in the middle of the finger) reflects ape-like characteristics.
Fossil hands of Australopithecus sediba and Homona Lady indicating that these South African hominins may have exhibited varying degrees of dexterity and climbing proficiency. Image credit: Tracy Kivell.
“This distinct pattern was unexpected and suggests that Homona Lady may have engaged different parts of its fingers for varied loading,” Dr. Syeda noted.
This unique loading pattern resembles certain grip types observed today, such as crimp grips used by rock climbers, where the surface is primarily grasped by the tips of the fingers.
Homona Lady also features unusually curved phalanges, particularly notable since this species coexisted with early members of our own species, Homo sapiens, indicating potential usage of hands for climbing.
Further research is necessary to ascertain whether Homona Lady utilized crimp-like grips for climbing; however, it is evident that throughout human evolution, there has been an ongoing requirement for using tools with enhanced dexterity for food processing on trees and rocks within the ancient South African landscape.
“This research offers greater evidence that human evolution is characterized by various ‘experiments’ balancing the demands of manipulation and movement within these historical environments, rather than a straightforward transition from upright walking to increasingly advanced tool use,” Dr. Kivell stated.
Survey results will be published this week in the journal Advances in Science.
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Samar M. Syeda et al. 2025. Bone distribution in the Faranjour cortex reveals variations in dexterity and climbing behaviors in Australopithecus sediba and Homona Lady. Advances in Science 11 (20); doi:10.1126/sciadv.adt1201
Source: www.sci.news
